This invention relates to a forward hand guard assembly for a semiautomatic rifle, such as the AR-15 rifle illustrated in FIG. 1.
The polymer forward hand guards or “forearms” provided as original equipment on many rifles are of large diameter and tubular in design requiring that the shooter's hand be wrapped around the guard (substantially beyond 50% of the circumference of the tube, as shown in FIG. 3b) to get a secure grip. Gripping a large diameter forearm this way is not ergonomic; it tires the hand and lower arm, which results in a poor grip and muscular fatigue. FIGS. 2b and 2c illustrate that the human hand is better suited to grip small diameter cylindrical objects where the fingers and hand can wrap fully around the diameter of the cylinder (locking the cylinder between the fingers and palm); while FIG. 2a shows the hand in an even more ideal position in the fully relaxed open position. FIG. 3a shows a handgrip according to the present invention: the hand is relaxed, in a configuration more like that of FIG. 2a. 
Unlike hunting or other military rifles which use a full stock, many semiautomatic rifles use three separate primary human interface points for stability, control and operation: the butt stock, the grip and the forward hand guard. The butt stock is used to ground the weapon against the body of the shooter, providing a point of stability; it also transfers recoil away from the weapon. The grip, sometimes referred to as a pistol grip, is a second point of control and stability for the weapon, and optimally positioning the shooter's trigger finger near to the weapon's operational controls. The forward hand guard serves as the third interface between the shooter and the weapon and is a primary point of support and control for weapon aiming.
The forward hand guard provides the main point of support for stabilizing the weapon by the shooter, allowing for accurate aiming and firing. Thus the hand and arm that interact with the forward hand guard are often referred to as the “support side” of the shooter, while the trigger hand is referred to as the strong or dominant side.
When a rifle is raised to the dominant side shoulder and aimed perpendicular to the shooter's body, the weight of the elevated stock, action or receiver, and barrel creates a cantilever effect, requiring a brace to counteract the weight and to stabilize the front of the weapon. The shooter's support side arm, with elbow bent and hand gripping the underside of the forward hand guard create the triangular brace needed to help transfer the outward extending weapon weight back to the shooter's body. Bracing the weapon in this manner also provides another point of stability for the weapon.
The act of extending the arm and hand out away from the body to support the weight of the rifle by gripping the forward hand guard, places physical demands on the shooter's anatomy. When the shooter is standing erect, the stability of the rifle becomes a function of a shooter's physical conditioning, technique, and comfort or ability to relax. Failure in any of these areas results in muscular fatigue, which commonly manifests itself through discomfort and shaking or quivering. Such movement is transferred to the rifle and compromises accuracy.
The fatigue created by the extension in arm and hand results in shaking or quivering of the muscles and causes movements in the weapon's barrel and sights, compromising accuracy.
The AR-15 rifle, M4 carbine, M16, AR-10 and like semiautomatic rifles share many common features and are all weapons that utilize the three separate primary human interface points described above. Because of the similarities in design and for the ease of this discussion we refer to this group of rifles simply as AR-15 rifles hereafter.
In the case of AR-15 type rifles, most are factory-equipped with one of three front hand guard designs: the traditional circular or oval polymer forward hand guard, an elongated tubular aluminum hand guard, or what is commonly referred to as an aluminum quad-rail hand guard. The purpose of these hand guards is (a) to provide a gripping surface for the shooter to secure the rifle, (b) to protect the forward hand from heat radiated from the barrel, and (c) to protect the operating components of the rifle. One feature that nearly all of these forward hand guards have in common is that they are all designed to be centered about the center of the rifle barrel's bore or center line.
A second common feature of many of these designs is that they all seek to maintain proper thermal clearances away from the hot barrel resulting in relatively large diameter profiles.
The fact that most forward hand guards are centered around the barrel's bore means that their widest points correspond with the two outer most surfaces of the barrel (i.e., three and nine o'clock positions). To maintain consistent insulating properties of the guard, the bottom of the guard or the six o'clock position is at least as far from the center of the barrel as at the three and nine o'clock positions. The combination of side width and the depth between the center of the barrel and the lowest point of the guard's profile require a deep grasp in order to properly secure the rifle with the support hand.
To grip these hand guards with a secure grip, the shooter must rest the bottom of the hand guard in the palm, while extending and wrapping fingers up and around the guard's large circumference. To achieve a secure grip, the ball of the shooter's finger tips must extend beyond 50% of the guard's circumference. The area above the 50% circumference can be referred to as the control surface area. It is this area that the fingers pull down against, capturing the guard between themselves and the palm. With the fingers positioned in this manner, having crossed beyond the 50% threshold, the forward hand sufficiently envelops the guard to provide a secure or locking grip. A locking grip is established when the fingers are able to pull an object in toward the palm. Conversely, if a shooter grips such guards over less than 50% of the circumference, with sufficient force, the guard will have a tendency to pop up out of the grasp of the shooter. This phenomenon is similar to what happens when one pinches a golf ball or other similar round object over less than 50% of the circumference. In such situations more force, only increases the likelihood of the guard jumping.
In addition to the general deep grasp problem described previously, aluminum quad rail guards are also hampered by the sharply machined “picatinny” accessory mounting rails that are machined into their side and bottom profiles. The harshness of the machined surfaces has resulted in manufacturers and aftermarket providers creating many after-the-fact solutions, the most common of which is the application of external covers that are meant to insulate the shooter's hand and to provide a smoother surface to grasp. The consequence to all these designs is that they all add even more circumference around which a shooter's hand must reach, further compounding the deep grasp problem.
Although physical conditioning and shooting technique are unique to each shooter, comfort can be directly influenced through proper ergonomic hand guard design.
The ideal hand guard design would provide a shallow grip, allowing for a relaxed hand and a positive gripping control edge to allow for a strong yet comfortable secure grip. These two ideal characteristics would be achieved by lowering the center of the guard's control surfaces from the barrel's center line, so that the guard is not constrained to the default widths and would also provide the room necessary to incorporate control edges for increased gripping.
The shallow grip used in an ideal hand guard profile would enable the shooter's hand to relax into a natural position. The universal natural position of a hand is a flat palm, semi-erect thumb and half-bent fingers. By incorporating a guard profile that allows for a relaxed natural hand position the stress on a shooter's forearm and hand is greatly reduced. Secondly, the ideal design would utilize well-defined, finite control edges as part of the shallow profile allowing the shooter to expend the minimum energy possible to maintain control of the weapon.
Because shooters and shooting conditions vary widely from one situation to the next, the ideal design would include various situation-specific hand grip profiles, and would allow these hand grip profiles to be quickly interchanged without the need for tools while in the field. Furthermore the tool-less assembly locking mechanism would provide a robust, secure function.
By creating a forward hand guard profile that allows the hand to relax and assume a natural position combined with control edges for an optimal secure grasp, a shooter will experience less fatigue and will allow for steadier and longer holds of the rifle.
It would improve the accuracy of a firearm, and the comfort of the shooter, to provide an ergonomic forward hard guard that overcame the problems mentioned above.